xen-blkfront: Cache feature_persistent value before advertisement

stable inclusion
from stable-v5.10.143
commit 186cb020bd3ab1248b5651e11de0d1abc696c65a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6D0U6

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=186cb020bd3ab1248b5651e11de0d1abc696c65a

--------------------------------

commit fe8f65b0 upstream.

Xen blkfront advertises its support of the persistent grants feature
when it first setting up and when resuming in 'talk_to_blkback()'.
Then, blkback reads the advertised value when it connects with blkfront
and decides if it will use the persistent grants feature or not, and
advertises its decision to blkfront.  Blkfront reads the blkback's
decision and it also makes the decision for the use of the feature.

Commit 402c43ea ("xen-blkfront: Apply 'feature_persistent' parameter
when connect"), however, made the blkfront's read of the parameter for
disabling the advertisement, namely 'feature_persistent', to be done
when it negotiate, not when advertise.  Therefore blkfront advertises
without reading the parameter.  As the field for caching the parameter
value is zero-initialized, it always advertises as the feature is
disabled, so that the persistent grants feature becomes always disabled.

This commit fixes the issue by making the blkfront does parmeter caching
just before the advertisement.

Fixes: 402c43ea ("xen-blkfront: Apply 'feature_persistent' parameter when connect")
Cc: <stable@vger.kernel.org> # 5.10.x
Reported-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: NSeongJae Park <sj@kernel.org>
Tested-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: NJuergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220831165824.94815-4-sj@kernel.orgSigned-off-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>
Reviewed-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/block/xen-blkfront.c

@@ -1852,6 +1852,12 @@ static void free_info(struct blkfront_info *info)
 	kfree(info);
 }
 
+/* Enable the persistent grants feature. */
+static bool feature_persistent = true;
+module_param(feature_persistent, bool, 0644);
+MODULE_PARM_DESC(feature_persistent,
+		"Enables the persistent grants feature");
+
 /* Common code used when first setting up, and when resuming. */
 static int talk_to_blkback(struct xenbus_device *dev,
 			   struct blkfront_info *info)
@@ -1943,6 +1949,7 @@ static int talk_to_blkback(struct xenbus_device *dev,
 		message = "writing protocol";
 		goto abort_transaction;
 	}
+	info->feature_persistent_parm = feature_persistent;
 	err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
 			info->feature_persistent_parm);
 	if (err)
@@ -2019,12 +2026,6 @@ static int negotiate_mq(struct blkfront_info *info)
 	return 0;
 }
 
-/* Enable the persistent grants feature. */
-static bool feature_persistent = true;
-module_param(feature_persistent, bool, 0644);
-MODULE_PARM_DESC(feature_persistent,
-		"Enables the persistent grants feature");
-
 /**
  * Entry point to this code when a new device is created.  Allocate the basic
  * structures and the ring buffer for communication with the backend, and
@@ -2394,7 +2395,6 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
 	if (xenbus_read_unsigned(info->xbdev->otherend, "feature-discard", 0))
 		blkfront_setup_discard(info);
 
-	info->feature_persistent_parm = feature_persistent;
 	if (info->feature_persistent_parm)
 		info->feature_persistent =
 			!!xenbus_read_unsigned(info->xbdev->otherend,